export const easingFuncs = {
	linear: function (k) {
		return k;
	},
	step: function (k, step){
		step = !step ? 10 : Math.ceil(step);
		var s = 1;

		while(k > s * (1 / step)){
			s++;
		}

		return s * (1 / step);
	},
	quadraticIn: function (k) {
		return k * k;
	},
	quadraticOut: function (k) {
		return k * (2 - k);
	},
	quadraticInOut: function (k) {
		if ((k *= 2) < 1) { return 0.5 * k * k; }
		return -0.5 * (--k * (k - 2) - 1);
	},
	cubicIn: function (k) {
		return k * k * k;
	},
	cubicOut: function (k) {
		return --k * k * k + 1;
	},
	cubicInOut: function (k) {
		if ((k *= 2) < 1) { return 0.5 * k * k * k; }
		return 0.5 * ((k -= 2) * k * k + 2);
	},
	quarticIn: function (k) {
		return k * k * k * k;
	},
	quarticOut: function (k) {
		return 1 - (--k * k * k * k);
	},
	quarticInOut: function (k) {
		if ((k *= 2) < 1) { return 0.5 * k * k * k * k; }
		return -0.5 * ((k -= 2) * k * k * k - 2);
	},
	quinticIn: function (k) {
		return k * k * k * k * k;
	},
	quinticOut: function (k) {
		return --k * k * k * k * k + 1;
	},
	quinticInOut: function (k) {
		if ((k *= 2) < 1) { return 0.5 * k * k * k * k * k; }
		return 0.5 * ((k -= 2) * k * k * k * k + 2);
	},
	sinusoidalIn: function (k) {
		return 1 - Math.cos(k * Math.PI / 2);
	},
	sinusoidalOut: function (k) {
		return Math.sin(k * Math.PI / 2);
	},
	sinusoidalInOut: function (k) {
		return 0.5 * (1 - Math.cos(Math.PI * k));
	},
	exponentialIn: function (k) {
		return k === 0 ? 0 : Math.pow(1024, k - 1);
	},
	exponentialOut: function (k) {
		return k === 1 ? 1 : 1 - Math.pow(2, -10 * k);
	},
	exponentialInOut: function (k) {
		if (k === 0) {
			return 0;
		}
		if (k === 1) {
			return 1;
		}
		if ((k *= 2) < 1) {
			return 0.5 * Math.pow(1024, k - 1);
		}
		return 0.5 * (-Math.pow(2, -10 * (k - 1)) + 2);
	},
	circularIn: function (k) {
		return 1 - Math.sqrt(1 - k * k);
	},
	circularOut: function (k) {
		return Math.sqrt(1 - (--k * k));
	},
	circularInOut: function (k) {
		if ((k *= 2) < 1) { return -0.5 * (Math.sqrt(1 - k * k) - 1); }
		return 0.5 * (Math.sqrt(1 - (k -= 2) * k) + 1);
	},
	elasticIn: function (k) {
		var s;
		var a = 0.1;
		var p = 0.4;
		if (k === 0) { return 0; }
		if (k === 1) { return 1; }
		if (!a || a < 1) { a = 1; s = p / 4; }
		else { s = p * Math.asin(1 / a) / (2 * Math.PI); }
		return -(a * Math.pow(2, 10 * (k -= 1)) * Math.sin((k - s) * (2 * Math.PI) / p));
	},
	elasticOut: function (k) {
		var s;
		var a = 0.1;
		var p = 0.4;
		if (k === 0) { return 0; }
		if (k === 1) { return 1; }
		if (!a || a < 1) { a = 1; s = p / 4; }
		else { s = p * Math.asin(1 / a) / (2 * Math.PI); }
		return (a * Math.pow(2, -10 * k) * Math.sin((k - s) * (2 * Math.PI) / p) + 1);
	},
	elasticInOut: function (k) {
		var s;
		var a = 0.1;
		var p = 0.4;
		if (k === 0) { return 0; }
		if (k === 1) { return 1; }
		if (!a || a < 1) { a = 1; s = p / 4; }
		else { s = p * Math.asin(1 / a) / (2 * Math.PI); }
		if ((k *= 2) < 1) {
			return -0.5 * (a * Math.pow(2, 10 * (k -= 1)) * Math.sin((k - s) * (2 * Math.PI) / p));
		}
		return a * Math.pow(2, -10 * (k -= 1)) * Math.sin((k - s) * (2 * Math.PI) / p) * 0.5 + 1;

	},

	// 在某一动画开始沿指示的路径进行动画处理前稍稍收回该动画的移动
	backIn: function (k) {
		var s = 1.70158;
		return k * k * ((s + 1) * k - s);
	},
	backOut: function (k) {
		var s = 1.70158;
		return --k * k * ((s + 1) * k + s) + 1;
	},
	backInOut: function (k) {
		var s = 1.70158 * 1.525;
		if ((k *= 2) < 1) { return 0.5 * (k * k * ((s + 1) * k - s)); }
		return 0.5 * ((k -= 2) * k * ((s + 1) * k + s) + 2);
	},

	// 创建弹跳效果
	bounceIn: function (k) {
		return 1 - easingFuncs.bounceOut(1 - k);
	},
	bounceOut: function (k) {
		if (k < (1 / 2.75)) { return 7.5625 * k * k; }
		else if (k < (2 / 2.75)) { return 7.5625 * (k -= (1.5 / 2.75)) * k + 0.75; }
		else if (k < (2.5 / 2.75)) { return 7.5625 * (k -= (2.25 / 2.75)) * k + 0.9375; }
		else { return 7.5625 * (k -= (2.625 / 2.75)) * k + 0.984375; }
	},
	bounceInOut: function (k) {
		if (k < 0.5) { return easingFuncs.bounceIn(k * 2) * 0.5; }
		return easingFuncs.bounceOut(k * 2 - 1) * 0.5 + 0.5;
	}
};